1. Field of the Invention
The present invention relates to a lifting apparatus capable of moving a platform vertically above a chassis so as to raise and lower an operator, an object or material located on the platform and, more particularly, to a lifting apparatus having a simple structure composed of one telescopic boom body and, yet, which can function in a manner equivalent to that of a conventional lifting apparatus having plural telescopic boom bodies, and also having a simple structure composed of a slave-operated detecting mechanism which is capable of synchronizing an inclining operation and an elongating operation of the telescopic boom body so as to raise the platform vertically relative to the chassis.
2. Description of the Prior Art
Lifting apparatuses are widely used for assembling, painting and repairing highway bridges, building construction or the like, which occur at elevated locations. In such apparatuses, an operator, an object or material is placed on a platform which is then raised or lowered.
A conventional lifting apparatus comprises a plurality of groups of arms, wherein each group of arms comprises a pair of arms which are pivotally connected at the central portion thereof. The plurality of groups of arms are assembled as one unit for forming a pantograph by combining the plurality of groups of arms vertically (a so-called scissors-type lifting apparatus). In the conventional arrangement of such an apparatus, it is necessary to lengthen each arm or to increase the number of groups of arms to be connected with one another in order to increase the height to which the platform can be raised. Accordingly, if a lifting apparatus capable of raising a platform to a higher position is designed, a plurality of groups of pantographs are required. This involved the problem that when the lifting apparatus is in its collapsed state wherein the linkage is folded, the platform is higher than is desired and the operation of loading the operator or the material is troublesome.
There was proposed another lifting apparatus capable of stretching one arm in the longitudinal direction thereof by inserting a plurality of booms stretchably into an arm (as disclosed in, e.g., Japanese Patent Application No. 56-134487 and No. 56-191065). In that lifting apparatus, middle booms are rotatably assembled at the central portion thereof in an X-shape, and two groups of middle booms are arranged in parallel with each other wherein an upper boom and a lower boom are respectively inserted into each middle boom so as to connect the chassis to the platform. This lifting apparatus has the problem that the number of booms is increased and the number of components is also increased, which involves laborious work for manufacture and assembly thereof, with consequent high cost.
In that apparatus, the sliding portions of each boom are increased in size which required slidable parts composed of synthetic resins, such as polyamide, for keeping in good condition the zone in which the sliding portions slide. These sliding parts should be regularly replaced with new parts. This involves an increase of the number of sliding parts and laborious work for inspection and maintenance, and high cost thereof.
To solve these problems, there was proposed another lifting apparatus comprising one elongatable boom and forming a Z-shape viewed from the side (Japanese Patent No. 59-95797). In this mechanism, it is necessary to control the direction in which the one elongatable boom extends and to control the inclination angle for inclining the one elongatable boom upwardly and downwardly, wherein both controls should be made to operate in synchronism with each other. Both controls necessitate a telescopic measuring unit for measuring the elongation amount of a telescopic boom body and an angle measuring unit for measuring the inclination angle of the telescopic boom body relative to the horizontal, wherein both units issue detecting signals which are used to control a first hydraulic cylinder for adjusting the inclination angle and a second hydraulic cylinder for controlling telescoping of the boom. It is complex to arrange these two measuring units in the lifting apparatus in view of the complicated assembly thereof. Furthermore, a calculating computer, such as a microcomputer and the like, is required for calculating the detecting signals issued by the two measuring units. The measuring units and the computer, respectively, are high cost items, which result in an increase of the manufacturing cost of the lifting apparatus as a whole. The cost of the measuring units and the computer significantly influence the total cost of a small size lifting apparatus because the cost price ratio of the computer is high relative to the total cost of the small size lifting apparatus. The Z-shaped lifting apparatus has the advantages that it requires fewer components compared with the conventional scissors-type lifting apparatus and the X-shaped lifting apparatus. However, this Z-shaped lifting apparatus has a drawback in that the controlling mechanism is complex and involves high cost because the telescopic boom body should be controlled in respect of inclination angle and lengthwise extension and contraction.
Accordingly, it is desired to provide a simplified control mechanism capable of lifting the platform vertically relative to the chassis without the need of measuring units for measuring the elongation of the telescopic boom body and the inclination angle of the telescopic boom body and without providing a computer for calculating the detecting signals issued by these measuring units. Particularly, the control mechanism can mechanically control the platform relative to the chassis without resorting to electronic instruments such as high-priced computers.
It is an object of the present invention to provide a lifting apparatus comprising a movable chassis, a platform disposed over the chassis, an elongated telescopic boom body extending between the chassis and the platform and comprising a plurality of boom sections which are telescopable into and out of the telescopic boom body in the longitudinal direction thereof, inclining means interposed between the chassis and the telescopic boom body for raising the telescopic boom body so that it is inclined with respect to the chassis, extension means housed within the telescopic boom body for telescoping the boom body to elongate and contract the same, wherein the platform, the telescopic boom body and the chassis are arranged to form a Z-shape when viewed from the side thereof and the telescopic boom body is telescopically moved and inclined relative to the chassis so as to move the platform vertically relative to the chassis while the platform is kept horizontal relative to the chassis, characterized in that: the lifting apparatus further comprises a slave-operated detecting mechanism including first and second winding drum, a first extension wire which has an end fixed to one lower surface of the platform and another end wound around the first winding drum and a second extension wire which has an end fixed to another lower surface of the platform and another end wound around the second winding drum.
It is an object of the present invention to provide a lifting apparatus comprising a tuning device including a winding drum and a detection wire which has an end fixed to one lower surface of the platform and another end wound around the winding drum.